A substantial number of phosphate-ester materials have been developed heretofore for use as fire-resistant hydraulic fluids, lubricants and the like; and while these materials possess many desirable properties, they have proved to be comparatively expensive; and this factor has encouraged reclamation of spent fluid rather than its discharge to waste. Environmental considerations, especially the reduction of phenolics and hexane-extractables in effluent waters, also indicate reclamation as the procedure of preference.
In use, phosphate-ester type fluids eventually become contaminated with such things as tramp oil, dirt, metal particles and metal salts of decomposed phosphate esters; and these fluids also degrade oxidatively with an increase in the acid number. Heretofore, used fluids of this nature have been reclaimed by treatment, for example, with aqueous caustic and by filtration through a material like fullers earth. Such procedures reduce solid and certain acidic contaminants but are not efficient in removing organic contaminants, especially those which contain combined iron or other metal salts.
Tramp oil contaminants adversely affect the fire-resistant character of the phosphate esters by lowering the autoignition temperature, flashpoint, fire point, and generally decrease the resistance to ignition by fire or heat sources. Additionally, the presence of tramp oil lowers the specific gravity of phosphate esters, which are ordinarily heavier than water, and increases the difficulty of separating or recovering them from effluent waters.
A common class of organic contaminants of phosphate-ester fluids includes the partial esters; and these may be present because of originally incomplete esterification or because of oxidation degradation. These partial esters, in turn, affect hydrolytic stability and water demulsability which reduce recoverability from effluent water streams. The partial acid esters also exhibit the unwanted faculty of complexing with such metal ions as calcium, magnesium, copper, aluminum and iron. These complexes tend to form solids or gels which, in turn, adversely affect the physical properties of the fluid and can even result in severe filtration problems in operating hydraulic systems.